Method of brightening electroplated coatings



Feb. 20, 1945.

ma HF" QUOIUII HUUI J. s. NACHTMAN 2,369,748

METHOD OF BRIGHTENING ELECTROPLATED COATINGS Filed March 50, 1942 Joli/z S Wadi/71011 Patented Feb. 20, 1945 UNITED STATES PATENT OFFICE METHOD OF BRIGHTENING ELECTRO- PLATED COATINGS 12 Claims.

The invention relates generally to the heat treatment of electroplated material, and more particularly to the heat treatment of strip steel electroplated with tin or tin alloys, for the purpose of brightening the coating.

Prior practice includes heat treating metal in a non-oxidizing or reducing atmosphere such as hydrogen or carbon monoxide, but where strip metal is heat treated continuously the use of such atmospheres is very expensive and requires excessively long time periods or long heat treating chambers or both. Moreover, such atmospheres are not well adapted for heat treating electroplated coatings such as tin, because of the rapid temperature changes required in the coated strip.

In order to brighten and improve the quality of the matte-like surface which is characteristic of electroplated tin coatings, in a minimum amount of space, I have determined that it is desirable to heat the coated strip rapidly and uniformly in a. non-oxidizing hydrocarbon medium to a temperature just above the melting point of 449.5 F. of tin for a short time to make the tin coating molten and close the pores thereof. While still in a non-oxidizing medium and without physically contacting anything else, the coated strip is then rapidly cooled to a temperature which is below the point of solidification of tin or below about 435 F., and then the coated strip is cooled further to below the temperature at which tin will oxidize, before being exposed to the atmosphere.

A method of brightening a tin or tin alloy coating, using a heat treating medium which boils below the melting point of the coating, for preheating, fusing and cooling the coating, is the subject of a separate application filed by me on March -30, 1942, Serial No. 436,783, and entitled Heat treatment of electroplated strip metal.

The subject of this application is a novel method of heat treating an electroplated tin or tin alloy coating, using a heat treating medium which boils above the melting point of the coating.

It is a general object of the present invention to provide a. novel method for brightening electroplated coatings of tin or tin alloys.

Another object is to provide a novel method for continuously heat treating strip electroplated with tin or tin alloys.

A further object is to provide a novel method for rapidly heating and cooling electroplated strip continuously to brighten the coating.

A still further object is to provide a novel atmosphere for continuously heat treating electroplated strip.

' These and other objects are accomplished by vaporizing a non-oxidizing medium of one or more hydrocarbons and which boils above the melting point of the coating, passing the strip through said vaporized medium at such a rate as to momentarily melt said coating by condensation of the vaporized medium on the strip, then immediately passing the strip into a cooled liquid bath of hydrocarbon medium to solidify the coating, and then passing the strip into another cooled liquid bath of hydrocarbon medium which is a solvent for said first and second media for cooling the strip below the oxidizing temperature of said coating.

Referring to the drawing forming part hereof, the figure is a diagrammatic cross sectional view of a preferred embodiment of apparatus for carrying out the invention.

In the drawing, the strip S, which has been previously electroplated with tin and rinsed, is shown emerging from a drier I. The strip S is heated in the drier to a. temperature below the solidification temperature of about 435 F. of the tin coating, and below the oxidizing temperature of tin.

The strip S is propelled through the apparatus by suitable means (not shown) and preferably passes over a roll 2 downwardly through a seal 3 which may be of soft material such as synthetic rubber or asbestos, and then into a vertical chamber 4 formed by refractory side walls 5 and 6 and top wall 1. The chamber 4 is the fusing compartment and is filled with heated vapor of a hydrocarbon medium which boils above the meltin point of tin. The medium is circulated preferably counter to the direction of travel of the strip, and due to the fact that the strip is at a lower temperature than that of the medium, the medium condenses on the surface of the strip and gives up its heat of vaporization to the strip, so as to quickly and uniformly raise the temperature of the strip and the coating thereon. The speed of travel of tl. strip through the chamber 4 is regulated so that the strip is in the chamber 4 only long enough to momentarily melt the coating and brighten the same.

Preferably, a heating chamber 8 for the hydrocarbon medium is formed adjacent to the fusing chamber 4, by extending the top wall 7 and providing a side wall 9. The lower part of the. heating chamber 8 is filled with the hydrocarbon medium in liquid form as indicated at X, and heating pipes ID are provided in the liquid bath for heating the liquid hydrocarbon X to vaporize the same. As the hydrocarbon medium X is vaporized a fan II circulates the vapor through opening I2 in the side wall into and through the fusing chamber 4 from which it reenters the heating chamber 8 through the opening I3 near the top of side wall 5.

Instead of preheating the strip S in drier I to 435 F., the strip can be preheated in the drier to about 200 to 225 F. and then passed tthrough the liquid hydrocarbon X to further preheat it to about 435 before it passes through the vaporized medium X in fusing chamber 4.

Preferably, the hydrocarbon medium X is a saturated or unsaturated aliphatic hydrocarbon or an aromatic hydrocarbon or a mixture of two or more which boils above the melting point of the tin coating on the strip, and preferably between 450 F. and 700 F., and which does not deposit carbon film or smudge when in contact with molten tin. Saturated and unsaturated aliphatic hydrocarbons and mixtures thereof include alkanes having a carbon chain of three or more atoms, olefins, and petroleum fractions or solvents. Aromatic hydro-carbons include coal tar fractions or solvents.

Petroleum and coal tar fractions in this boiling range are light hydrocarbons as distinguished from heavy oils, and have high rates of thermoconductivity as compared with heavy oils, but do not oxidize or vaporize to any extent at room temperatures. They have high thermostability and do not decompose or crack when heated to a soldering temperature or as high as 550 F., which accounts for the fact that no smudge is left when said fractions are in contact with molten tin.

For the purposes of illustration, I will describe the use of a high boiling petroleum solvent or fraction known as Mentor-28 as the medium X. Mentor-28 is a petroleum fraction with boiling points in'a range of 510 F., to 650 F., a flash point of approximately 255 F. and a fire point of approximately 294 F. This material has a viscosity of 4.83 centipoises at 25 C., has practically no vapor pressure or evaporation loss at 25 C., and has a gravity range between 35 to 38 A. P. I.

The fusing compartment 4 communicates at its lower end with a tank T having the Wall 5 as one of its side walls, and a bottom wall I4 and another side wall I5. Preferably the tank has a partition wall l6 and the wall 6 of compartment 4 extends down into the tank between the wall 5 and the partition wall I6. Between the walls 5 and I6 the tank is filled with a liquid hydrocarbon medium indicated at X which is preferably the same hydrocarbon medium as X, and a passage I! through wall 5 provides communication between the liquid mediums X and X so that the liquid level in the lower part of chamber 4 is the same as in the lower part of chamber 8.

The strip S passes downwardly into the liquid hydrocarbon X between cooling (oils I 8 on opposite sides of the strip, and the cooling coils maintain the medium X at a lot ered temperature so as to immediately cool the tin coating below its olidification temperature before it contacts anything. The strip then passes under a roll I9, u wardly between cooling coils I8 and out of the liquid hydrocarbon X where it preferably passes between squeegee rolls for removing the excess liquid X from the surface of the strip. The cooling coils I8 and I8 are preferably regulated to maintain the liquid X at a temperature of about 130 F.- a

Obviously, the hydrocarbon X can be a different hydrocarbonfrom the medium X and included in the group of saturated and unsaturated aliphatic hydrocarbons and aromatic hydorcarbons or mixtures thereof. If X is a different hydrocarbon medium from X, the passage I1 is omitted so that the two baths of liquid hydrocarbons X and X are not connected, and the media X and X must have sufficiently different boiling points so that they can be separated by simple distillation.

Also while the vaporizing chamber 8 is shown and described as being conveniently adjacent to the fusing compartment 4, it is obvious that the vaporizing compartment could be located remote from the fusing compartment and the vaporized hydrocarbon conducted thereto.

From the squeegee rolls 20 the strip S passes over a roll U and then downwardly into a liquid hydrocarbon medium indicated at Y contained in the compartment of the tank formed between walls I5 and I6. The hydrocarbon medium Y is preferably a different hydrocarbon taken fro-m the group of saturated and unsaturated aliphatic hydrocarbons and aromatic hydrocarbons and mixtures thereof, and should have a boiling point below the temperature at which tin will oxidize; and the hydrocarbon Y may be hexane with a boiling point somewhere between F. and F. Hexane is a solvent for Mentor-28 which is preferably used as the hydrocarbon medium X and X, and is also a solvent for any other high boiling point hydrocarbons which may be used as media X and X.

The temperature of the hexane Y is maintained below its boiling point preferably by cooling pipes I8" to keep it in a liquid state and the strip S passes down into the liquid Y, under a roll 22 and upwardly out of the liquid Y over a roll 23. Preferably a partition wall 24 depends from the top wall 25 of the tank into the hydrocarbon Y between the rolls 2I and 23 and between the downwardly and upwardly moving portions of the strip S in the liquid Y.'

As the strip passes through the hydrocarbon Y, the film of hydrocarbon X and X on the strip is dissolved by the hydrocarbon Y and as the strip leaves the hyrocarbon Y it passes between squeegee rolls 2G to remove excess film before the strip passes over the roll 23.

From the roll 23 the strip passes through an opening 21 in wall I5 and into a small tank 28 containing a low boiling liquid hydrocarbon Y selected from the group of saturated and unsaturated aliphatic hydrocarbons and aromatic hydrocarbons and mixtures thereof, and the strip passes through the liquid hydrocarbon Y under roll 29 and then preferably through squeegee rolls 30 and out of the tank 28 through a seal 3I.

In tank 28 the liquid hydrocarbon Y is preferably hexane to which about one-half per cent by weight of palm oil or other vegetable oil has been added, and the liquid Y is kept at a temperature at or below room temperature preferably by cooling pipes 28' so as to further cool the strip as it passes through the same; As the strip passes through the squeegee rolls 30 the film of liquid hydrocarbon Y is spread uniformly and thinly over the strip, and as the strip emerges through the seal 3I the hexane will evaporate from the strip surface leaving an imperceptible oil film thereon. The percentage of vegetable oil added to the liquid Y may be varied somewhat depending upon the thickness of oil film desired to be left on the strip surface.

13p to o' ifii. p 204. CHFMlSTRY, ELECTRICAL i; W

YN AV .1 LRGYi 1 U 9,869,748 3 A distillation system or conventional design terial through said vaporized coal tar fraction at indicated at 32 may be used to separate the carry such a rate as to momentarily melt said coating over of the liquid X from the liquid Y. Thus by condensation of said coal tar traction on said the liquid Y with the carry over X is conducted material, and then passing the material immethrough pipe 33 to the distillation apparatus 32, diately into a cooled liquid bath of hydrocarfrom which the separated liquid X is pumped bon medium to solidify the coating. through pipe 34 and pump 35 back to the com- 4. The method of heat treating material elecpartment containing the liquid X. The pure troplated with a coating of tin, which includes liquid Y is pumped from the distilling apparatus vaporizing a coal tar fraction which boils be- 32 through a pipe 36 and pump 31 to sprays 38 m tween about 450 F. and 700 F., passing the mawhich spray the strip as it emerges from liquid terial through said vaporized coal tar fraction at Y to remove all traces of liquid X and X from such a rate as to momentarily melt said coating the Surface of e tr pby condensation of said medium on said material, If difierent high boiling point hydrocarbons and then passing the material immediately into are used for X and X, there will be a carry over a cooled liquid bath of said coal tar fraction of the liquid X on the strip surface into the maintained at a temperature of about 130 F. liquid X, and a distillation system similar to 5. Improvements in the plating of metals that indicated at 32 can be used to separate the which comprise electrolytically depositing a coatliquids X and X and return them to their proper ing of tin on a ferrous strip, and then continucompartments. ously passing the metal coated strip thru the The strip carryin rolls 2, l3, 2|, 22, 23 and vapor of a petroleum hydrocarbon having a boil- 29 are made of a suitable material such as poling point above the melting point of tin until the ished steel, or polished chrome plated steel, which coating of tin is raised to a temperature above its will not mar or scratch the surface of the strip, lti p nt y nde s ti of s d ydr rand these rolls are preferably driven at the speed Don v p 0n the n S ac of travel of the strip to prevent any marring f 6. The method of heat treatin e l e cthe surface due to slippage between the strip and troplated with a' coating of tin for brightening the roll surface. the tin surface, which includes vaporizing a first Liquid hydrocarbons X and Ymay be the same y o n m Which boils above the hydrocarbon in which case the partition wall 16 melti g P t O exposing the material to may be omitted together with rolls 22 and 23, so i v p riz d medium to mom n ri y melt said that the strip passes directly from roll 2| into Coating and brighten t Same y eondensetien the tank 28. of said first medium on said material, then im- If desired, the hydrocarbon medium in any of mediately passing the material into a cooled liqthe compartments may be introduced therein by uid bath of a second hydrocarbon medium to someans of sprays or jets directed against the strip. lidify e C t nd t n passing the material The term hydrocarbon medium" as used hereinto a cooled liquid bath of a low boiling hydroin means a saturated or unsaturated aliphatic carbon medium which is a solvent for said first hydrocarbon or an aromatic hydrocarbon, or a d Second mediaa mixture of two or more of said hydrocarbons, 0 7. The method of heat treating material elecwhich boils above the melting point of tin and troplated with a coating of tin, which includes preferably between 450 F. and 700 F., and which vaporizing a hydrocarbon medium which boils does not deposit carbon film or smudge when in between about 450 F. and 700 F., passing the contact with the molten coating. material through said vaporized hydrocarbon While I have described the heat treatment of medium at such a rate as to momentarily melt electroplated strip metal, the invention may be said coating by condensation of said hydrocarbon applied to strip sheets, sheets, wire and the like, medium on said material, then passing the mawithout departing from the scope of the invention terial immediately into a cooled liquid bath of as defined in the appended claims. hydrocarbon medium to solidify the coating, and Iclaim: then passing the material into a cooled liquid 1. The method of heat treating material elecbath of hydrocarbon medium which dissolves the troplated with a coating of tin, which includes film of hydrocarbon medium left on the surface vaporizing a petroleum fraction which boils beof said material. tween about 450 F. and 700 F., passing the 8. The method of heat treating material elecmaterial through said vaporizing petroleum fractroplated with a coating of tin, which includes tion at such a rate as to momentarily melt said vaporizing a hydrocarbon medium which boils coating by condensation of said petroleum fracbetween about 450 F. and 700 F., passing the tion on said material, and then passing the mamaterial through said vaporized hydrocarbon terial immediately into a cooled liquid bath of medium at such a rate as to momentarily melt hydrocarbon medium to solidfy the coating. said coating by condensation of said medium on 2. The method of heat treating material elecsaid material, then passing the material immetroplated with a coating of tin, which includes diately into a cooled liqui bath of Said y vaporizing a petroleum fraction which boils becarbon medium maintained at a temperature of tween about 450 F. and 700 F., passing the about 130 F., and then removing the film of said material through said vaporized petroleum from. hydrocarbon medium from the surface of the tion at such a rate as to momentarily melt said material, coating by condensation of said medium on said 9. The method of continuously heat treating material, and then passing the material imme ferrous strip electroplated with a coating of tin, diately into a cooled liquid bath of said petrowhich includes vaporizing a hydrocarbon meleum fraction maintained at' a temperature of 7 dium which boils between about 450 F. and 700 about 130 F. F., passing said strip through said vaporized hy- 3. The method of heat treating material elecdrocarbon medium at such a rate as to momentroplated with a coating of tin, which includes tarily melt said tin coating by condensation of vaporizing a coal tar fraction which boils besaid medium on said strip, and then passing the tween about 450 F. and 700 F., passing the mastrip immediately into a cooled liquid bath of said hydrocarbon medium to solidify the coating.

10. The method of continuously heat treating ferrous strip electroplated with a coating of tin, which includes vaporizing a hydrocarbon medium which boils between about 450 F. and 700 F., passing said strip through said vaporized hydrocarbon medium at such a rate as to momentarily melt said tin coating by condensation of said medium on said strip, and then passing said strip immediately into a cooled liquid bath of said hydrocarbon medium maintained at a temperature of about 130 F.

11. Improvements in the plating of metals which comprise electrolytically depositing a coating of tin on a metal base stock and then continously passing the metal coated stock thru the vapor of a hydrocarbon medium having a boiling point above the melting point of tin until the coating of tin is raised to a temperature above its melting point by condensation of the said hydrocarbon vapor on the tin surface.

12. Improvements in the plating of metal which comprise electrolytically depositing a coating of tin on a metal base stock, then continuously passing the metal coated stock thru the vapor of a hydrocarbon medium having a boiling point above the melting point of tin until the coating of tin is raised to a temperature above its melting point by condensation of said hydrocarbon vapor on its surface, and then immediately passing the stri thru a liquid bath of hydrocarbon medium maintained at a temperature of about 130 F. to solidify the tin.

JOHN S. NACHTMAN. 

